Here’s a hint: one channel features a “news” duo who famously tilt to the left, while the other is known for foisting The Situation and Snooki on an unsuspecting public.

Comedy Central’s prime-time audience fell 19% in the four weeks through Oct. 21, while MTV’s viewership declined 32% in the same period, according to Nielsen.Signs of slight ratings erosion were evident at both channels earlier this year, but the recent numbers show a much greater decline. So far this year, Comedy Central’s average daily viewership is down 10% while MTV’s is off 18%. Nickelodeon’s audience, meanwhile, is down 23% for the year to date although the drop-off in September was narrower than in previous months….MTV’s ratings falloff has come even before the channel loses its popular “Jersey Shore.” The reality show is in its last season and the network hasn’t developed any monster hits to replace it.